Thousands of jubilant New Yorkers flocked to the site of the 9/11 terror attack during the night to celebrate the killing of Osama bin Laden by U.S. troops, but for families who lost someone on 9/11 bin Laden's death was greeted with a mix of elation and sadness.

Revelers waved American flags, chanted "USA" and sang patriotic songs during the night. Others popped champagne corks, climbed trees, swung from lampposts and street signs in a spontaneous party that started shortly after President Obama announced bin Laden's death before midnight Sunday.

"Tonight is a great night," said Rocco Chierichella, the retired firefighter who famously handed President George W. Bush a bullhorn when he visited the smoldering wreckage of the twin towers nearly 10 years ago.

"People are releasing some of that jubilation," he told ABC News steps from where he told President Bush that he couldn't be heard.

"I can hear them all," Chierichella said of the revelers. "Let's hear it for the U.S. Army. Tonight is for them."

Mayor Michael Bloomberg rallied New Yorkers at a press conference this afternoon.

"Osama bin Laden is dead and lower Manhattan is pulsing with new activity...Osama Bin Laden is dead and New York City's spirit has never been stronger," said Bloomberg.

"It is heartwarming news," said Alice Hoagland, whose son Mark Bingham died on United Flight 93, the plane that crashed into a Pennsylvania field after being hijacked by terrorists. "It is a form of closure to know that Osama bin Laden is facing his God."

Hoagland is also worried about the future.

"I am concerned that his al Qaeda has taken new shape and new form…that's probably the dreadful specter that we will be facing as the American people go forward," she said.

Lee Ielpi, a former New York City firefighter who lost his firefighter son when the Twin Towers fell, thanked the military for some measure of justice, but warned about the mood becoming too celebratory.

"This is one man. The cancer has been eliminated, but there are still people out there who need to be brought to justice," he said. "I do hope that this brings some comfort to not just the families but worldwide, the ones who have lost loved ones to terrorists."

The news of bin Laden's death tears open the wounds for some 9/11 families.

David McCourt once described the pain of losing his 4-year-old daughter, Juliana, and wife, Ruth, on Sept. 11 as paralyzing sadness and anger that prevented him from moving forward. News of the al Qaeda mastermind's death brought memories of their loss flooding back to him.

"Justice had to be served at some point…for those of us who lost so much on 9/11…it was elation and also for me sadness attached to it because it was a reminder of what I lost," he said.

McCourt's daughter and wife were on their way to Disneyland when their flight was hijacked by bin Laden's terrorists and flown into the World Trade Center.

"This morning, here's a reminder and a sadness that comes over you of what you lost. I am at a different place. I can look at my wife and daughter in one sense, a better sense, and just thank God for allowing them to be in my life for that short period of time rather than a 100 percent of that anger. It's difficult and feelings go back and forth," he said.

For Mary Fetchet who lost her son on Sept. 11, 2001, the military success is a measured step in her healing process.

"Disbelief certainly was the first emotion that I felt... comfort, appreciation for President Obama and the military installations that brought Osama bin Laden to justice," Fetchet said.

Osama bin Laden's Death Sparks Celebrations Nationwide

For most Americans, the news that bin Laden was tracked down and killed 10 years after he attacked the World Trade Center and the Pentagon was a mix of celebration and pride.

At Ground Zero this morning, one woman held up an iPad serving as makeshift poster, which read "Obama: 1, Osama: 0." Muslim women in head scarves and Muslim men in turbans and long beards carrying American flags, mixed with retired firefighters, service members in uniform and college students.

For New York City firefighters who lost hundreds of their own on Sept. 11, firehouses erupted over the news. Some drove their trucks into the heart of Times Square this morning.

"Osama bin Laden was responsible for killing 343 members of the FDNY on Sept. 11, 2001. Tonight, in firehouses throughout the city, our members are grateful for the news, and thankful to all the brave members of the U.S. military that had a role in this successful operation," said Fire Commissioner Salvatore Cassano in a statement.

The news literally brought a Mets-Phillies game in Philadelphia to a standstill. It was announced over the loud speaker, and then the crowd started screaming, "USA...USA."

On college campuses across the nation, students too young to remember much before 9/11 put their own stamp on history.

One picture sent to "Good Morning America" from Penn State showed thousands of students pouring into the streets. More photos and video from schools like Iowa State and West Virginia show massive crowds of students cheering and waving American flags.

At West Point, cadets, not even 10 years old when the World Trade Center came down, were seen chanting across their campus.

In Dearborn, Mich., a heavily Middle Eastern suburb of Detroit, the Associated Press reported a small crowd had gathered outside the town's City Hall waving American Flags and cheering.

By morning, the celebration at Ground Zero had been replaced by construction workers rebuilding the site who were buoyant over the news of bin Laden's death.

"I can't explain it but it feels different today," said Victor Colon, a concrete laborer who laid the foundation for the Freedom Tower under construction.

"Everyone seems a little happier. They've got more motion in their step.... When you come to work here every day after every day you start to forget what happened. But today you remember why we're here."